Binary Star Systems

The majority of stars are not single stars, they come in pairs of two or more stars (even in star clusters, containing thousands of stars - globular clusters), orbiting around a common gravitational centre and following Kepler's Laws.
Some stars are easy to detect, others require different measures for detection. On the night sky, some stars may appear to be a binary starsystem, but they are coincidentally placed close to each other.

At first, astronomers thought all stars simply appeared to be double stars, but in 1802 Sir William Herschel discovered that many of the stars that appeared close to each other actually had changed in position relative to each other.
Binary stars that can be distinguished through an optical telescope are called visual binaries. An example of an optical binary is the star Mizar, which is the second star from the left in the handle of the constellation The Big Dipper, or more precisely: Ursae Majoris, The Big Bear. Mizar is actually a binary system which can be distinguished with the naked eye, and is a fine target for amateur astronomer who wish to test their eyesight.
The second component of the star is called Alcor, or Mizar B. Later studies have revealed that both stars are in turn binaries, which makes the entire Mizar complex a system of four stars! The discovery was made using spectroscopy, which is a method used to detect unseen companions. Binaries discovered with this method are called spectroscopic binaries.
When detected, it is relatively easy to calculate the mass of the binary star system, which is more difficult for single stars.
The closest star to our sun, located 4.6 light years away, is Proxima Centauri, which is actually a system of three stars. Alfa-Centauri is the brightest of the three.

Binary starsystems can vary greatly and are very interesting to study. Each component can have an affect on the other partner's course of life. Systems containing a white dwarf can display a nova, which is an energetic explosion, which can be been at great distances.
Other systems, may contain a neutron star, or even a black hole, which strips off gas from its companion star. The gas is accelerated towards the compact object and heated to more than one million degrees Kelvin, which is enough to produce x-rays!

Here, in this part of the Nova Celestia gallery you can read and view information about some interesting kinds of binary stars, like cataclysmic variables, pulsars, x-ray binaries and eclipsing binaries.